The present invention relates to a driving arrangement wherein an endless belt is driven by a rotary drive wheel and, in particular, to a positive drive engagement between the belt and drive wheel.
In order to assure the mobility of wheeled vehicles on soft loose terrain, such as sand or snow for example, the wheels should support vehicle load without serious sinkage into the ground through the use of endless belts. When such belts are installed on tandem wheels they provide an increased area and length of contact and thereby improve flotation and traction.
Endless belts are known which are formed of an assembly of steel elements such as links, pins, shoes, etc. A simpler form of endless belt comprises an elastic belt such as reinforced rubber which provide a smoother ride and imparts less damage to the road surface than steel tracks. Elastic belts are driven by drive wheels either by a friction or positive engagement therewith. In the case of a friction drive, the belt must be pre-loaded in tension so as to firmly engage the drive wheel upon subsequent contraction. However, in order to obtain sufficient friction, such a strong tensioning must be achieved that the wheel bearings may be subjected to excessive loading.
Furthermore, the driving wheel and idler wheels are located at ground level to act as ground support wheels. Such an arrangement leads to bull-dozing and steering difficulties, especially on soft terrain. When operating on wet muddy terrain, the driving friction deteriorates and the drive transmission suffers from serious slippage.
The disadvantages associated with friction drives can be avoided by a positive drive wherein teeth on the elastic belt mesh with teeth on the drive wheel. Such a drive eliminates the need to tension the belt and thus there exists no possibility of overloading the belt and wheel bearings. Furthermore, the positive engagement between the teeth eliminates any chance of slippage. Also, the track can operate on a smaller wrap angle over the driving wheel which allows the driving wheel and idler to be located above ground level. That arrangement of the wheels provides better mobility at high speeds and less resistance to turns. However, such a drive involves drive wheels with a relatively small tooth pitch in order to maximize the number of teeth in mesh. That structure requires relatively high dimensional tolerances and accurate alignment, which characteristics are very costly to achieve and difficult to maintain under off-road conditions. Furthermore, the vulnerability of the teeth to shocks minimizes the maximum velocity which is attainable. Consequently, the utility of positive drive belts has been somewhat limited.
It would be further desirable to provide a positive drive for an endless belt/rotary drive wheel arrangement which eliminates the problems discussed above.